The role of aeolian dust in ecosystems
The recent upsurge in research attention to aeolian dust has shown that dust transport systems operate on very large spatial and temporal scales, and involve much larger quantities of sediment than was previously realized. An inevitable consequence of this is that researchers from a range of neighbouring disciplines, including ecology, are beginning to realize that this new knowledge has important implications for their study areas. In the present paper, we examine the ecological implications (real and potential) of this expanding knowledge of dust transport systems, with a particular emphasis upon the Australian dust transport system. We track these ecological effects from source to sink. At source, wind erosion-soil-vegetation relationships are often dominated by temporal changes in rainfall. Nine years of measurements in the Channel Country of the Lake Eyre Basin, Australia show that vegetation and soils in dune fields can recover from drought, whereas on inter-fluve grasslands uni-directional and negative successional vegetation changes can result from wind erosion during drought. On floodplains, both wind erosion and vegetation responses are complicated by flood frequency. Up to 1999 flooding of saline claypans did not increase vegetation but did increase wind erosion through the supply of alluvial fines. However, after three floods within as many months vegetation became established and wind erosion rates were dramatically reduced. Wind erosion research attention is now gradually turning from the physical to the organic content of eroded dusts. In Australia organic matter content can reach 65% by mass, but this cannot be explained by removal of soil organic matter alone. Biological soil crusts not only stabilize soils against wind erosion but contribute to some of the organic dusts. The role of dust as a vector for pathogens is an area which deserves greater research attention in the future. Downwind from source, we show that dust contributions to soils are more widespread and more variable (in time and space) than earlier work on dust-derived loess soils has suggested. Recent studies also show positive dust impacts upon nutrient budgets within distant forest ecosystems, and significant contributions to river nutrient loads, especially in the arid sectors of internally draining river basins. The number of studies of dust impacts upon marine ecosystems is increasing dramatically. Studies of dust within Antarctic ice cores combined with dust modelling provide compelling evidence that increased soluble iron-rich dust inputs to the Southern Ocean have stimulated phytoplankton populations. Modern process studies are, however, yet to clearly demonstrate these relationships. Finally we examine the potential for major dust impacts upon global climates, using its positive and negative effects upon solar radiation and precipitation as examples of the complexity and importance of this new research area.